The present disclosure relates to a solid-state image pickup device, a method of driving a solid-state image pickup device, and an electronic instrument, and more particularly to a solid-state image pickup device, a method of driving a solid-state image pickup device, and an electronic instrument which are capable of operating in a global shutter mode for moving images.
Electronic shutters for image sensors which read charges stored in photodetectors through MOS transistors include a rolling shutter. Since the rolling shutter reads signal charges from each pixel or each pixel row at a time, all the pixels do not have the same exposure period in which charges are stored in the photodetectors. If a moving subject is imaged by an image pickup device with a rolling shutter, then the captured image tends to suffer a distortion.
There has been proposed a global shutter in which the pixels include respective charge holders and charges stored in photodetectors of the pixels are transferred altogether to the charge holders and held therein as signal charges until they are read from each pixel row at a time, thereby allowing all the pixels to share the same exposure period (e.g., see Japanese Patent Laid-open No. Hei 11-177076, hereinafter referred to as Patent Document 1).
A pixel which includes a photodetector and a charge holder has a smaller photodetector area and a smaller maximum charge quantity (saturated charge quantity) stored in the photodetector than a pixel which includes no charge holder. Even if the photodetector is designed for a larger area in the pixel which includes the photodetector and the charge holder, a charge quantity that is eventually handled as a signal charge by the pixel is up to the maximum charge quantity that is held by the charge holder which is of a smaller area. Consequently, it is desirable that the photodetector and the charge holder be designed for substantially the same maximum charge quantity (area). With the photodetector and the charge holder being designed for substantially the same maximum charge quantity (area), however, the maximum charge quantity is about one-half of the maximum charge quantity handled by the pixel which includes no charge holder. The pixel which includes the photodetector and the charge holder is thus unable to increase the charge quantity handled thereby.
One proposed solid-state image pickup device stores charges in a photodetector and a charge holder during an exposure period by providing an overflow path between the photodetector and the charge holder or having a potential barrier with a variable potential between the photodetector and the charge holder (e.g., see Japanese Patent Laid-open No. 2009-268083, hereinafter referred to as Patent Document 2). The proposed solid-state image pickup device makes it possible for the pixel which includes the photodetector and the charge holder to increase the charge quantity handled thereby up to the saturated charge quantity stored by the pixel which has no charge holder.